But a few years ago, the billionaire investor admitted in a Congressional hearing that he didn't know much about credit rating agency Moody's or the credit ratings market in general, the New York Times reported at the time.
Now that knowledge gap seems to have come home to roost. On Wednesday Bloomberg reported that Warren Buffett's investment firm Berkshire Hathaway may have just lost up to $291.5 million on its Moody's holdings.
According to Bloomberg, Berkshire owned a 13 percent stake in Moody's as of Sept. 30. The credit rating agency's stock price took a beating this week due to the government's recent lawsuit against S&P, Moody's main competitor, for allegedly inflating its mortgage bond ratings during the run-up to the financial crisis.
The stock may yet bounce back: The government probably won't sue Moody's. The Justice Department included the firm at first in its three-year investigation of credit rating agencies but later dropped Moody's from the probe, a source familiar with the investigation told McClatchy.
Don't feel too bad for Buffett. The world's fourth-richest man has a net worth of $52.4 billion, according to the Bloomberg Billionaires Index.